Patent Document 1 (identified below) discloses an existing DAB converter. In the DAB converter described in Patent Document 1, a full-bridge circuit is connected to each of a primary winding and a secondary winding of a transformer and the switching phase difference between the two full-bridge circuits is appropriately controlled to perform transfer of power.
Patent Document 1: U.S. Pat. No. 5,355,294.
With the converter described in Patent Document 1, switching loss can be reduced by performing zero voltage switching (ZVS) using leakage inductance from the transformer and parasitic capacitance of a semiconductor device. However, since the ZVS range is restricted and reactive current is increased in proportion to the difference between an input-output voltage ratio and the turn ratio of the transformer, efficiency may be reduced when performing the ZVS. For example, when the input-output voltage ratio is high and a load connected to an output terminal is lightly loaded, the reactive current that does not contribute to transmitted power may be increased to degrade the efficiency.